Honors Biology: Unit 11-Evolution

LaMarck

believed that evolutionary changes were caused by organisms actively adapting themselves to environmental conditions

Law of Use and Disuse

-the more an animal uses a particular structure the more prominent and well-developed the structure will become

-the less a structure is used the less prominent and well-developed it will become

Inheritance of Acquired Characteristics

belief that traits an organism has developed could be passed onto offspring

Malthus

-realized that populations tended to increase geometrically and limited supplied of resources could not keep up with demands of increasing population

-sets up a competitive situation

-his ideas influenced the theories of Charles Darwin

3 Major Points of Darwin’s Theory of Descent with Modification through Natural Selection

1) Species over-reproduce

2) Competition for limited resources occurs

3) Variations exists among individuals making some better able to compete for limited resources than others; those who gain the most resources reproduce more; their offspring skew the gene pool resulting in evolution of the species

Adaptation

favorable genetic variation; makes an organism more likely to survive and reproduce

Fitness

measure of reproductive success; how many surviving offspring are produced

Speciation

accumulation of favorable adaptations over time which result in the formation of a new species

Genetic Equilibrium

-condition in which allele frequencies in a population do not change from one generation to the next

-rate of occurrence of traits remains constant

-no evolution occuring

Directional Selection

extreme phenotype becomes a favorable adaptation

Stabilizing Selection

-average phenotypes become more favorable and extreme phenotypes become more unfavorable

-usually inhibits (holds back) the rate of evolution because of a narrowed range of variation

Disruptive Selection

-rare form of natural selection

-extreme phenotypes become more favorable than average phenotypes

-creates 2 separate subpopulations

Hardy-Weinberg Principle

outlines conditions necessary for genetic equilibrium in a population to be maintained (no evolution)

Allelic Frequency

term used to describe how often a particular allele occurs in a population

Gene Pool

all of the possible alleles that exist in a population

Conditions Necessary to Maintain Genetic Equilibrium

1) no mutations

2) individuals may neither enter nor leave a population (emigration-leaving) (immigration-entering)

3) large population (prevents genetic drift)

4) individuals mate randomly; no selective breeding

5) no natural selection (equal survivorship)

Genetic Drift

-a change in the allelic frequency of a small population brought about by chance

2 important causes of Genetic Drift

Founder’s Effect: population started by a few pioneering individuals moving into a new region (reduces genetic variation)

Bottleneck Effect: a small group of surviving members of a population breeding together (reduces genetic variation)

Why Evolution Occurs

-because these conditions cannot ever be met, no genetic equilibrium can ever exist, therefore evolution must occur

-allelic frequencies are never in equilibrium = gene pools change over time = phenotype frequencies are changing = EVOLUTION

Hardy Weinberg Mathematical Formula

p - frequency of dominant alleles in population

q - frequency of recessive alleles in population

p² - frequency of homozygous dominant genotype in population

2pq - frequency of heterozygous genotype in population

q² - frequency of homozygous recessive genotype in population